Atmospheric Sciences & Global Change Staff Awards & Honors

Long-Lived Traveling Particles to be Tracked

PNNL researcher awarded project to study climate-relevant particles

Unseen
by the human eye are plentiful microscopic particles, small but mighty
polycyclic aromatic hydrocarbons, or PAHs, constantly emitted into the air from
a variety of combustion sources. Power plants, forest and brush fires,
wood-burning fireplaces, and even the backyard barbeque launch a soupy swell of
chemicals into the atmosphere, all bundled into aerosol particles. These trace aerosol
components are highly toxic and are believed to increase human risk for cancer.
They enter the atmosphere, but how do they get there? And where do they go?

What's Been Missing from the Models?

Current
climate models fail to explain how these aerosols are carried through the
atmosphere, traveling far away from their originating source. However, scientists
have made progress with the recently discovered, new molecular-scale
interactions between the health-concerning PAHs and climate-concerning secondary
organic aerosols, or SOAs.

From natural and man-made emissions to atmospheric particles, secondary organic aerosol particles are born in the atmosphere and affect climate around the world. Many of these particles include hitch-hiking polycyclic aromatic hydrocarbons, or PAHs, both health-concerning and long-lived, often traveling far from the emitting source. A new research project will track these particles to understand how to better represent their effects in climate models.

SOAs
are particles formed in the atmosphere when natural emissions, like those from
aromatic pine trees meet with carbon-based emissions from coal-burning power plants
or vehicle emissions to form a new particle. Recent laboratory measurements that discovered the connection between
PAHs and SOAs encouraged Dr. Manish Shrivastava, a Department of Energy-sponsored early-career
atmospheric researcher at Pacific Northwest National Laboratory, to conduct modeling studies to understand the effects of PAH-SOA interactions.

Shrivastava
is leading a team to develop new modeling algorithms, or formulas climate
models can use, to understand interactions too complex to observe in real life
using a grant from PNNL's Laboratory Directed Research and Development (LDRD)
program. Shrivastava and his team will develop these algorithms based on the newly
found molecular-scale atmospheric processes, translating the understanding of the
long-range transport of PAHs for climate models. Further, they will delve into how
the PAHs interact with natural particles in the atmosphere, to ultimately update
climate models.

How Do they Live Long and Prosper?

Following
measurements from previous studies, the team will develop novel modeling
algorithms that show how PAHs are trapped in larger organic particles-essentially
hitching a free ride as the SOAs travel far distances. This synergistic PAH-SOA
interaction shows how the climate-relevant
SOA particles act as efficient vehicles to protect and carry cancer-causing PAHs,
capturing and shielding them from chemical degradation and evaporation as they
travel. In turn, the PAHs increase the number and weight of the SOA particles. This
newly found bond between the two may be the reason why both the PAH and SOA
particles live so long and travel so far.

Their
research, expected to wrap up in in the next two years, promises to demonstrate why the new SOA particle
treatments are needed to better inform policy decisions related to both climate
and human-health resilience in a changing world.

Shrivastava's
LDRD grant funds up to two years of study into the effects of PAHs on the
climate. His was one of 5 projects awarded out of 90 proposals submitted at the
lab in 2015. PNNL's LDRD program is designed to enable research staff to pursue
innovative ideas that enhance core scientific and technical disciplines. Thus,
the LDRD emphasizes cross-disciplinary research to promote a synergy between
science and technology.

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In short....

In one sentence: Dr. Manish Shrivastava
is leading a team to develop new modeling formulas climate models can use to
understand atmospheric particle interactions too complex to observe in real
life using a grant from PNNL's Laboratory Directed Research and Development program.